Photosensitive resin compositions have been put to practical use as materials for pattern formation in large quantity and in many fields (see “Photopolymer Technology”, ed. Tsuguo Yamaoka and Gentaro Matunaga, published by THE NIKKAN KOGYO SHIMBUN, LTD., (1988)). Polymeric photosensitive materials possess excellent resolution and, at the same time, can realize setting of a broad exposure range, for example, by selecting a light wavelength and, thus, can be properly utilized according to applications. Further, the resin layer patterned by light irradiation plays an important role as a resist material in chemically, physically or dynamically etching the base material. The photosensitive resin composition has also been put to practical use as printing plate materials for relief plates, intaglio plates, lithographic plates, and stencil printing plates wherein a light pattern is transferred by ink.
By taking advantage of the above features, the photosensitive resin composition has been used as photoengraving materials in a wide range from submicrons to centimeters.
In general, in the case of polymeric photosensitive materials, a pattern is formed by development treatment based on a change in physical properties such as solubility which is based on a change in chemical structure between exposed parts and unexposed parts. Alternatively, when the photosensitive resin composition is used as a surface covering treatment material, the function of protecting the base material is developed by a change in physical properties based on a significant change in chemical structure upon exposure. The change in chemical structure in the above resin is based on a mere photochemical reaction, as well as on the whole of a variety of secondary chemical reactions induced by the photochemical reaction. As a result, for example, the solubility of the resin layer in a solvent before and after exposure can be arbitrarily selected.
When a relief pattern is formed from a photosensitive resin by development with a solvent, the use of water, which is most inexpensive and safe, as a solvent is indispensable because of direct relation to environmental problems such as working environments and measures against wastes. In order to use the water-developable photosensitive resin, for example, as a screen printing plate material, the resultant pattern should be resistant to solvents and water derived from ink. In particular, a pattern formed by development with water is in many cases hydrophilic, and, thus, photosensitive resins, which exhibits significantly improved water resistance, have been desired.
The use of a photosensitive resin composition comprising a photoradical polymerizable aqueous emulsion and a photocrosslinking agent has been extensively adopted as a method for improving water resistance. Examples of such photosensitive resin compositions include compositions comprising a photoradical polymerizable compound and an aqueous resin emulsion dispersed in poly(vinyl alcohol) (patent document 1: Japanese Patent Laid-Open No. 230568/1994), and water developable compositions produced by emulsifying an ethylenically unsaturated compound and a radical photoinitiator in poly(vinyl alcohol) and incorporating a photocrosslinking agent in the emulsion (for example, patent document 2: Japanese Patent Laid-Open No. 121852/1974, patent document 3: Japanese Patent Laid-Open No. 108003/1975; patent document 4: Japanese patent Laid-Open No. 107343/1984, and patent document 5: Japanese patent Laid-Open No. 127377/1993). In this case, even when a photoradical polymerization reaction proceeds, any crosslinked structure is not formed in the poly(vinyl alcohol) per se. Accordingly, photocrosslinking agents such as bichromates and diazo resins are added. The bichromate-type photosensitive resin, however, contains heavy metal ions, which cause environmental contamination, and has poor storage stability. For this reason, a two-component type should be adopted, and the utilization of the bichromate-type photosensitive resin is limited and is excluded. On the other hand, the use of a water-soluble diazo resin as a photocrosslinking agent poses problems that the photosensitization speed is low, and, due to the limitation of light transmission by coloring of the exposed parts, the water-soluble diazo resin is unsuitable for a thick photosensitive layer. In addition, the long-term storage stability is so poor that a two-component type, in which a photosensitive resin composition is prepared immediately before use, should be adopted. That is, in all the cases, inconvenience of two-component type is not eliminated.
Poly(vinyl alcohols) substituted by a photocrosslinkable residue typified by strylpyridinium have been proposed as one-component-type water-developable photosensitive resins (patent document 6: Japanese Patent Laid-Open No. 23941/1980 and patent document 7: Japanese Patent Laid-Open No. 62905/1980). Further, compositions comprising the photocrosslinkable poly(vinyl alcohol) and an aqueous emulsion have been proposed for screen printing plate making (patent document 8: Japanese Patent Laid-Open No. 62446/1980 and patent document 9: Japanese Patent Laid-Open No. 102232/1984). Since, however, the photocrosslinkable residue is hydrophilic, the water resistance of the relief pattern is unsatisfactory. To overcome this problem, the following proposals have been made. One of them is a composition containing a photoradical polymerizable emulsion added thereto (patent document 10: Japanese Patent Laid-Open No. 10243/1985, patent document 11: Japanese Patent Laid-Open No. 10244/1985, and patent document 12: Japanese Patent Laid-Open No. 247637/1985). Further, a method, in which dichromic acid or a diazo resin as a water soluble photocrosslinking agent is added to this type of composition, has also been proposed (Japanese Patent Laid-Open No. 10245/1985). Furthermore, the addition of phosphoric acid or a phosphorous acid compound has been proposed for improving the water resistance (patent document 13: Japanese Patent Laid-Open No. 229005/1989). Furthermore, a water-developable photosensitive resin composition comprising a water-soluble photoacid generator added to poly(vinyl alcohol) and an acid-reactive crosslinking agent has also been proposed (patent document 14: Japanese Patent Laid-Open No. 319080/1997).
So far as the present inventors know, however, the crosslinked poly(vinyl alcohol) has unsatisfactory water resistance from the viewpoint of maintaining the hydrophilicity. Accordingly, when screen printing is carried out using an aqueous ink, stencils produced using this composition cannot yet simultaneously realize satisfactory solvent resistance and water resistance. Further, problems involved in one-component-type photosensitive resin compositions, which satisfy various properties including mechanical strength, remain unsolved.
Patent document 1: Japanese Patent Laid-Open No. 230568/1994
Patent document 2: Japanese Patent Laid-Open No. 121852/1974
Patent document 3: Japanese Patent Laid-Open No. 108003/1975
Patent document 4: Japanese Patent Laid-Open No. 107343/1984
Patent document 5: Japanese Patent Laid-Open No. 127377/1993
Patent document 6: Japanese Patent Laid-Open No. 23941/1980
Patent document 7: Japanese Patent Laid-Open No. 62905/1980
Patent document 8: Japanese Patent Laid-Open No. 62446/1980
Patent document 9: Japanese Patent Laid-Open No. 102232/1984
Patent document 10: Japanese Patent Laid-Open No. 10243/1985
Patent document 11: Japanese Patent Laid-Open No. 10244/1985
Patent document 12: Japanese Patent Laid-Open No. 247637/1985
Patent document 13: Japanese Patent Laid-Open No. 229005/1989
Patent document 14: Japanese Patent Laid-Open No. 319080/1997